The chemical structure of three isoenzymes of cathepsin D from the porcine spleen will be studied. Isoenzyme II which has a molecular weight of 35,000 can be obtained in largest quantity using affinity chromatography. The sequence study will be approached with initial cyanogen bromide cleavage. The fragments will be purified and studied for sequence separately. Isoenzyme I and III will be studied comparatively. The sequence information will define their structural and functional interrelationships.